Sinus

Part of speech: noun

Pronunciation: /ˈsaɪ.nəs/

Definitions

1. A cavity in the cranial structure that plays a role in mucus production and sound resonance while also acting as a channel for air in the respiratory system
2. An anatomical air-filled space within the skull that facilitates vocal resonance and reduces skull weight, often linked to respiratory functions
3. A hollow space within the skull that is involved in producing mucus, aiding in sound modulation, and serving as a passage for air in breathing processes

Etymology: The Latin "sinus" meant a bend, curve or hollow, most famously the fold of a toga pulled up to form a pocket, and that sense of an enclosed hollow is what the anatomical word inherited. English took "sinus" directly from Latin as a learned borrowing, so it kept the original form rather than being worn down through French as many older words were. The surprise is that "sine," the mathematical term for a trigonometric ratio, is the same word. Both descend from the Latin for a curve, and the trigonometric sense came about through a translation chain from Arabic and Sanskrit words for a half-chord, a line stretched across a curve. English thus contains a true doublet: one Latin noun split into an anatomical cavity and a geometric function.

Synonyms: cavity, channel, duct